The behavior of Drosophila towards light (phototaxis) can be used to select mutants that interrupt the nervous system of the fly. In principle, a collection of such mutants can be used to describe the neural circuitry of a reflex or fixed action behavior, or the cellular basis of endogenous behaviors, such as biological rhythms. Using the method of counter current distribution to separate flies on the basis of their behavior, large numbers of sex linked mutants have been obtained and genetically analyzed. Of these, mutants at seven cistrons code for defects in fly vision, as described by changes from the normal electroretinogram (ERG). Some mutants are degenerative and resemble certain heritable human diseases. This application includes plans to continue the analysis of these sex linked, to search for autosomal behavioral mutants, and to search for mutants interrupting larval phototactic behavior in order to identify the larval photoreceptor and its cellular basis. Preliminary electrophysiological analyses of these mutants will be attempted. Techniques will be developed to facilitate the genetic mapping of these mutants to precise locations on the chromosomes. Techniques using gynandromorphs and somatic crossing over yield mosaic flies and can be used to effect genetic change in the developing (somatic) cells in Drosophila to determine where the mutant lesion is located, and when in development the mutant gene is normally expressed.